Previous studies have demonstrated that both family dysfunction and internet addiction (IA) are associated with a higher risk of adolescent depression. However, no study has yet investigated the mechanisms involved. This study aims to explore the mediation and interaction roles of internet addiction (IA) between family functioning and depressive symptoms among adolescents in rural China.A multi-stage, stratified cluster, and random sampling was conducted among 3343 adolescents in rural China from October 27 to November 6, 2020. Depressive symptoms, IA, and family functioning were assessed using the Epidemiologic Studies Depression Scale (CESD), the Internet Addiction Test (IAT), and the Family Adaptation Partnership Growth Affection and Resolve Index (APGAR), respectively. Correlation analysis was performed by binary logistic regression. The study employed a four-way decomposition method to explore the potential mechanisms of family functioning on depressive symptoms.The results indicated that family functioning and IA were associated with adolescents' depressive symptoms. The interaction between family functioning and IA accounted for 74 % of the association between family functioning and depression symptoms, while direct effects accounted for 24 %. The "proportion eliminated" (76.11 %) was substantially larger than "proportion mediated" (7.36 %).The cross-sectional design limited to identify the causal relationship among the variables.We found that family dysfunction synergizes with IA to contribute to the high risk of adolescent depression. Prioritizing at preventing IA in adolescence could be an effective way to mitigate the adverse effects of family dysfunction on depression.Copyright © 2024. Published by Elsevier B.V.